In a power-producing steam turbine, the turbine shaft is usually supported at multiple locations along its length by sleeve bearings. A sleeve bearing's inner diameter is slightly larger than the outer diameter of the shaft so as to provide clearance for shaft rotation. For example, the inner diameter of the bearing may be 0.010 inch larger than the outer diameter of the shaft, thereby providing a clearance of 0.005 inch between the shaft and the bearing when the shaft is centered in the bearing.
When a shaft is rotating at its nominal operating speed, the shaft usually rides on a hydrodynamic wedge of oil between the bearing and the shaft. If the shaft develops an abnormal vibrational mode while rotating, the outer surface of the shaft may contact the inner surface of the bearing and cause damage to the shaft and the bearing. To avoid such situations, it is important for operational personnel to be able to monitor the position of a rotating shaft with respect to the surfaces of the sleeve bearings in which it rotates.
What is needed, therefore, is a tool for providing a visual depiction of a shaft rotating within multiple sleeve bearings, which depiction indicates the relative spacing between the outer surface of the shaft and the inner surfaces of the bearings and indicates the average center line of the shaft at each bearing location.